Railway car braking apparatus in which one or more air operable piston and cylinder assemblies, each cylinder containing one piston, is supported from the car truck and which, when supplied with air at above atmospheric pressure, applies forces to the brake rigging and to the brake shoes engageable with the four wheels supporting the truck which supports the car body is known. See, for example, U.S. Pat. Nos. 3,107,754 and 4,312,428.
Some of the prior art systems require mounting of the piston and cylinder assembly or assemblies on the truck bolster which increases the installation time, labor and cost. To obtain the braking forces required, a cylinder of relatively large diameter is used and the available space for location of such a cylinder is relatively limited. Also, some prior art systems require openings in the truck bolster for the passage of components of the system, and because different trucks, built by different builders, may not have openings in the bolster of the proper size or location for the passage of such components, either the prior art systems cannot be installed on some of such trucks or a new opening or openings must be provided in the bolster which is undesirable.
In addition, in prior art systems, the slack adjuster, i.e. the device which is used to limit piston stroke with brake shoe wear, usually is located in the braking assembly so that it measures piston stroke which addresses only brake force losses due to piston stroke length and the accompanying air pressure drop in the cylinder but does not address the problem of the loss of force at the brake shoes due to a change in direction of a lever or a bell crank angularity. If the mechanisms downstream of where the slack adjuster measures piston stroke length is "fouled", the slack adjuster may properly compensate for piston stroke change but may result in insufficient or no braking force on the shoes.
Furthermore, prior art braking systems usually require a relatively large and strong brake shoe beam which transmits the force of the piston to shoes engageable with two different pairs of truck wheels. Such beams are relatively expensive and occupy a large part of the space available on the truck for braking apparatus.